1. Field of the Invention
The present invention relates to an optical disk drive which records data on and reproduces data from an optical disk, such as a magneto-optical disk. Particularly, the present invention relates to a focus offset, a tracking offset, and control of a laser output value.
2. Description of the Related Art
There has hitherto been known an optical disk drive which records data on and reproduces data from an optical disk, such as a magneto-optical disk, and an optical disk drive of play-only type. Such an optical disk drive effects focus and tracking control operations. During the focus and tracking control operations, offset adjustment is performed for compensating for individual characteristics of an optical disk drive or for making the optical disk drive compliant with conditions of use. More specifically, a focus offset and a tracking offset are adjusted.
Offset adjustment is performed only once at startup of an optical disk drive; that is, when an optical disk is loaded into the optical disk drive. In relation to a focus offset, at the time of startup of the optical disk drive, an offset value is set to a value at which an RF signal is maximized. In relation to a tracking offset, at the time of startup of the optical disk drive, an offset value is set to a value at which a tracking error signal obtained in an on-track state comes to the center of a tracking error signal obtained in an off-track state. Focus and tracking control operations are performed while the thus-set offset values are taken as references until the optical disk is unloaded from the disk drive.
Further, an output value of laser emitted from a pickup is set also at the time of startup of the optical disk drive. More specifically, the laser output value is set such that a data error rate is minimized.
The related-art optical disk drive sets a focus offset, a tracking offset, and a laser output value only at startup. Hence, if changes have arisen in the internal temperature of an optical disk drive because of changes in the ambient temperature of the optical disk drive or those in the temperature of a board provided in the optical disk drive or the like, changes will arise in an offset characteristic of a circuit or in an optical property of a pickup. As a result, the set offset values and the laser output value will deviate from optimal values. Particularly in the case of a portable optical disk drive, set offset values and laser output values may greatly deviate from optimal values when the optical disk drive is transported from indoors to outdoors.
For example, in relation to a focus offset, a relationship between a focus offset value and an error rate at 25° is different from that at 65°, as shown in FIG. 6. Further, in relation to a tracking offset, a relationship between a tracking offset value and an error rate at 25° is different from that at 65°, as shown in FIG. 7. Optimal offset values change in accordance with temperatures. If offset values deviate from appropriate values, recording and reproducing operations may fail to be performed properly.